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Mobile 3-foot mobile antennas

Discussion in 'CB Antennas' started by DeedleD, Feb 16, 2019.

  1. DeedleD

    DeedleD Member

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    Everyone knows that 3-foot antennas for CB band severely restrict RF performance and efficiency and provide a very narrow bandwidth, but it's something us city dwellers have to settle for... I've owned Wilson Little Wil and Sirio Turbo 800, both of which are 3-foot tall and work surprisingly well! Without an antenna tuner, both antennas achieved flat SWR mid-band and 2:1 at the edges. With an antenna tuner (MFJ-945E) I was able to get them down to 1.2:1 at the edges. This is barefoot, using Uniden 980 SSB and CRE 8900.



    I then started experimenting with more power (dumped to dummy load, of course!) to see how both antennas reacted and to see if they were really able to handle what the manufacturer claimed. This is just my experience, others might have different results. Both antennas handled 100W dead-key like a champ with 1.5:1 mid-band and 3:1 SWR at the edges. The antenna tuner brought these values down to 1.2:1 mid-band and 1:5:1 at the edges.

    At 150W Wilson reached it's limit and would not tune but Sirio still performed great with no SWR increase. At 200W Sirio started to experience SWR anomalies, during dead-key the SWR would start out low but immediately start creeping up. At 200W same thing, but it would rise faster. I didn't try any higher and called it a day. Since the amp was able to produce 300W I started searching for another 3-foot antenna that could handle the load... The answer was Midland LUX700 which is rated for 600W @ 50% TX 50% RX duty cycle.

    I ordered it from a company called Avera for $60 and it shipped from Europe via FedEx International. I was surprised when it arrived in mere 3 days, to the Midwest USA! It's just a few inches taller than the Sirio and is heavier, maybe due to larger gauge coil. The whip seems to be the same diameter. I was able to tune it to 1:1 SWR mid-band without much difficulty. With and without the antenna tuner it had the same SWR performance as Wilson and Sirio, barefoot, and with 100W.

    The moment of truth, at 200W no change in SWR and the needle is not creeping up. Same at 250W and at 300W, so I think we have a new winner! So far I'm very impressed with this antenna, low profile and handles 300W like a champ. As a bonus, when you key up the base of the antenna lights up which is kinda cool.

    Anyway, this is my experience, your results may vary.

    [​IMG]
    [​IMG]
     

  2. loosecannon

    loosecannon Sr. Member

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    be careful running a mag mount with that much power.
    they've been known to mess up the paint underneath them when used with a linear.
    LC
     
  3. w9cll

    w9cll W9WDX Amateur Radio Club Member

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    So your secret is use a cheap antenna an feed it a lot of power?
     
  4. BJ radionut

    BJ radionut Supporting Member and 6m addict

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    Not to mention, if the antenna load heats up from Hi VSWR and melts thru the plastic shroud and flashes over to the alm luggage rack coated in salt residue...
    Yes paint damage is highly possible on any mag mount regardless of power used...add Salt and Ice to the equation and it's just a matter when not if...
    All the Best
    Gary
     
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  5. 357magnum

    357magnum Sr. Member

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    No disrespect Chris , but probably not the smartest thing I ever did but , for 5 years I ran a POS RS mag mount feeding it 250w w/ no damaging results . Now I wonder why that thing never shot off my roof like a Bottle Rocket ?:LOL: I just got lucky ( & smarter ) I guess .:whistle:o_O;) But still running a mag mount Stryker Sra-10 .
     
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  6. psycho

    psycho Running a special on our rooms!

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    A tri magnet mount for a 3 foot antenna made my night!
    Just pull the magnet mount off once a month and clean the mag and roof, that will help eliminate damage.
     
    #6 psycho, Feb 17, 2019
    Last edited: Feb 17, 2019
    357magnum and Tallman like this.
  7. w9cll

    w9cll W9WDX Amateur Radio Club Member

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    There is nothing wrong with using a mag mount. I am questioning a three foot antenna with 300w. I can't help but say a properly mounted 108" whip with 100w would smoke his setup.
     
  8. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    Your experiment is flawed. You cannot test antennas by dumping your wattage into a dummy load.
    Also you cannot tune the antenna properly by tuning to a power level. You have harmonics out the Wazoo.
    You really need to tune to the primary frequency of operation. The SWR change you are seeing with increased power out put is the result of harmonics.
     
  9. TheRealPorkchop

    TheRealPorkchop Certified Sith Pimp

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    Yeah I wanted to ask how you test am antenna into a dummy load, I want a drawing of that. Please.
     
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  10. hotrod

    hotrod Well-Known Member

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    get a skipshooter 3 footer . rated at 3000.. doubt that will handle that much but for 19.00 bucks wy not. advailable at copperelectronics.com
     
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  11. 357magnum

    357magnum Sr. Member

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    I agree Chris , A whip was always my favorite , but these days I just can't bring my self to drilling a hole in the side of my vehicle . In my younger years I had NP because most of my vehicles didn't cost me much , now w/ the cost .... I just can't do it !;):LOL:
     
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  12. DeedleD

    DeedleD Member

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    Thanks, I've also heard that from others, I figured it's a 20 year old truck so I'm not that concerned with paint discoloration, besides I'm not planning on running that much power all the time, it was just a test to see if the antenna could handle it.

    Yeah, it's overkill for a 3-footer but I like testing different antenna setups and some are taller so the tri-mount comes in handy in that regard.

    I agree, a 108" whip would definitely smoke this setup, but I have height restriction and need to keep it low profile. Over the weekend I tested communicating with base from shopping center parking lot 8 miles away, with 100W and I was able to hit it with a 9 pound signal so I'm happy with this performance. It helps that the base station is equipped with an 18-foot Sirio 2016 5/8 wave antenna standing atop a 25-foot Channel Master telescoping mast but it's still not bad for a city with lots of obstacles in the way, trees, houses, hills, etc.

    The dummy load comment was not serious and the harmonics are attenuated via Kenwood LF-30A low-pass filter. I did tune it to the primary frequency of operation which is almost middle of the band (ch 23) and I'm getting 1.2:1; on ch1 and ch40 it's 1.5:1 with it tuned to mid bad. I can attain 1.2:1 on channel 1 and 40 by re-tuning if I wanted.

    When I'm traveling for vacation, I switch to a rear mount 4-foot Firestick antenna which seems similar to that skipshooter you mentioned. Unfortunately half the antenna remains below the roofline and it picks up some noise from the fuelpump, but it's better than nothing!

    [​IMG]
     
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  13. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    Then why is your SWR going up when you add power? Harmonics that are not being filtered out? How do we know what to believe?
     
  14. w9cll

    w9cll W9WDX Amateur Radio Club Member

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    Something is wrong here, with normal 4 watts.you should get this performance. Antenna is everything not wattage.
     
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  15. DeedleD

    DeedleD Member

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    It could be common mode current on the outside of the coax or because the radio is too close to the antenna, since this is a mobile application. Like I said it’s not perfect but it works.
     

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